(1) Field of the Invention
The present invention relates to a battery in which at least one of the anode means and the cathode means is formed of an acetylene high polymer having a fibrous microcrystalline (i.e., fibril) structure and a high bulk density and which is characterized in that said battery has a high energy density whereby a longtime discharge is possible, the levelness of the discharge curve is good, the cycle life is good, self-discharge is reduced and reduction of the weight and size can easily be accomplished.
(2) Description of the Prior Art
An acetylene high polymer obtained by polymerizing acetylene in the presence of a so-called Ziegler-Natta catalyst comprising a transition metal compound and an organic metal compound has an electrical conductivity of the semiconductor region, and therefore, it is an organic semiconductor material valuable as an electric or electronic element. However, since the acetylene high polymer prepared according to the above process does not become molten even by heating and since it is readily subject to oxidative deterioration under heating, the polymer cannot be molded according to the customary molding method adopted for ordinary thermoplastic resins. Furthermore, a solvent capable of dissolving therein this acetylene high polymer has not been found. Therefore, molded articles of acetylene high polymers have heretofore been prepared only according to the following two processes.
(A) A powdery acetylene high polymer is compression-molded.
(B) Under specific polymerization conditions, polymerization is carried out to obtain an acetylene high polymer in a film form having a fibrous microcrystalline (fibril) structure and a high mechanical strength (see Japanese patent publication No. 32581/73).
The process (A) is defective in that the molded articles exhibit a low mechanical strength. Although the process (B) is advantageous over the process (A) in that a molded article having a much higher mechanical strength can be prepared, the bulk density of the acetylene high polymer molded article is 0.60 g/cc at the highest (the true density of the acetylene high polymer is 1.20 g/cc) and only a porous film is obtainable according to the process (B).
There also is known a process in which a gel-like acetylene high polymer is freeze-dried and the resulting acetylene high polymer in a foam form is compressed to obtain a compressed porous film having a bulk density of 0.4 g/cm.sup.3 (see Polymer Preprints, 20, No. 2, pages 447-451, 1979). The bulk density of the compressed porous film of the acetylene high polymer according to this process is 0.4 g/cm.sup.3 at the highest, and this compressed porous film is substantially similar to the acetylene high polymer film prepared according to the process disclosed in Japanese patent publication No. 32581/73.
It is known that when a powdery acetylene high polymer, prepared according to the process (A), is treated with an electron-accepting compound (acceptor) such as BF.sub.3, BCl.sub.3, HCl, Cl.sub.2, SO.sub.2, NO.sub.2, HCN, O.sub.2 or NO, the electrical conductivity is increased 1000 times at the highest and when this acetylene high polymer is treated with an electrondonating compound (donor), the electrical conductivity is reduced to 1/10,000 in an extreme case [see D. J. Berets et al., Trans, Farady Soc., 64, 823 (1968)].
It also is known that when an acetylene high polymer film, obtained according to the process (B) is chemically doped with an electron acceptor such as I.sub.2, Cl.sub.2, ICl, IBr, AsF.sub.5, SbF.sub.5 or PF.sub.6, or an electron donor, such as Na, K or Li, the electrical conductivity of the acetylene high polymer film can freely be controlled in a broad range of from 10.sup.-8 to 10.sup.3 .OMEGA..sup.-1.cm.sup.-1 [see J. C. S. Chem. Commu., 578 (1977), Phys. Rev. Lett., 39, 1098(1977), J. Am. Chem. Soc., 100, 1013 (1978) and J. Chem. Phys., 69, 5098 (1978)]. Furthermore, use of this doped acetylene high polymer film as a material of a cathode of a primary battery has already been proposed [see Molecular Metals, NATO Conference Series, Series VI, 471-489 (1978)].
In addition to the above-mentioned chemically doping process, there has already been developed an electrochemically doping process in which an acetylene high polymer is electrochemically doped with an anion dopant, such as ClO.sub.4.sup.-, PF.sub.6.sup.-, AsF.sub.6.sup.-, AsF.sub.4.sup.-, CF.sub.3 SO.sub.3.sup.- or BF.sub.4.sup.-, and a cation dopant, such as R'.sub.4 N.sup.+ (in which R' stands for an alkyl group), to obtain electrically conductive acetylene high polymers of the p-type and n-type [see J. C. S. Chem. Commu., 1979, 594. C & EN, Jan., 26, 39 (1981) and J. C. S. Chem. Commu., 1981, 317]. Furthermore, a re-chargeable secondary battery, utilizing electrochemical doping of a acetylene high polymer film prepared according to the process (B) has been reported [see Paper Presented at the International Conference on Low Dimensional Synthetic Metals, Hersinger, Denmark, 10-15, August, 1980]. This battery comprises as the cathode and the anode, two acetylene high polymer films prepared according to the process (B), and when these electrodes are immersed in a solution of lithium iodide in tetrahydrofuran and are connected to a 9-V direct current source, lithium iodide is electrolyzed to dope the acetylene high polymer of the cathode with iodine cations and the acetylene high polymer of the anode with lithium anions. This electrolytic doping corresponds to the charging step. When the two doped electrodes are connected to a load, the lithium ion reacts with the iodine ion to generate electric power. It is reported that in this rechargable secondary battery, the open circuit voltage (Voc) is 2.8 V and the short circuit current density is 5 mA/cm.sup.2. When a solution of lithium perchlorate in tetrahydrofuran is used, the open circuit voltage is 2.5 V and the short circuit current density is about 3 mA/cm.sup.2.
In this rechargable secondary battery, an acetylene high polymer, allowing reduction of the weight and size of the electrodes, is used as the electrode material. Accordingly, this battery, which is attractive as a rechargable secondary battery, has a high energy density, can easily be reduced in weight and size, and can be manufactured at a low cost. However, since the acetylene high polymer, used as the electrode in such known battery, is an acetylene high polymer in the form of a porous film having a low bulk density, which is prepared according to the above-mentioned process (B), this battery is inevitably defective in the following points.
(i) The short circuit current (Isc) is reduced to zero within a very short time (within about 3 minutes) at the time of discharge. Namely, the discharge time is very short.
(ii) Since the amount of the dopant doped is 6 mole % the at highest, based on the recurring unit CH of the acetylene high polymer constituting the electrode, the energy density or discharge capacity is limited.
(iii) The levelness of the discharge curve is poor.
(iv) The deterioration of the acetylene high polymer is advanced by repetition of the charging and the discharging, and no economically satisfactory cycle life can be obtained.
(v) The self-discharge is prominent.
Accordingly, the uses of such a battery, in which the electrode material is comprised of an acetylene high polymer in the form of a porous film prepared according to the process (B), is considerably limited. Therefore, development of a cheap battery which ensures a long-time discharge with a high energy density or discharge capacity, a good levelness of the discharge curve, a good cycle life with reduced self-discharge and in which the weight and size can easily be reduced, has been desired in the art.